


Mismatched Mates

by TheBeastsWrite (orphan_account)



Category: Supernatural
Genre: Alpha Dean, Biting, M/M, Mates, Prompt Fill, Rough Sex, Self Lubrication, Tentacles, cumming untouched, i have no idea how to tag this, merman!cas, octo!Dean, omega cas
Language: English
Status: Completed
Published: 2015-08-04
Updated: 2015-08-04
Packaged: 2018-04-13 00:20:14
Rating: Explicit
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 1
Words: 1,323
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/4500504
Author URL: https://archiveofourown.org/users/orphan_account/pseuds/TheBeastsWrite
Summary: <blockquote class="userstuff">
              <p>For Rebel-Cas on tumblr who wanted Octo!Dean and Merman!Cas I hope you enjoy this!</p>
            </blockquote>





	Mismatched Mates

**Author's Note:**

> So this might just be the strangest thing I've ever written and I think I love it?
> 
> Come and find me on tumblr at thewolf-inred.tumblr.com
> 
> I hope you enjoy! :)

Dean and Cas? They’d been courting for many moons now. Honestly he can’t even give you an exact count but it feels like forever and yeah, he’s one hell of a lucky guy. 

Cas was gorgeous, all sleek and fast, pretty blue tail that shimmers when the light filters just right through the water, messy black hair that waves as he swims, fins glinting playfully. 

He was an omega, a hunter for his school of Mer-peeps, they’d met when some assholes from the deep sea tried taking some turf of theirs. Dean’s damn corals had almost been damaged. 

Anyway, it wasn't a smooth sailing in the beginning. He’d never met a mer-person before and Cas had never even heard of the octo’s so you can imagine the confused angry hissing that occurred. After a while though, after talking and meetups after sundown they’d.. well, they’d kinda fallen hard. 

Cas had bought him this pretty sea-shell necklace as a first move, offered it with a flush across his cheeks and a duck of his head and Dean had melted, wrapped it around his thickest tentacle as his people did with tokens of affection. 

In return he’d hunted, gotten the biggest damn sword fish he could find and shared their first meal together, after that? Well it’s pretty simple. They considered each other mates. 

Dean’s pop hadn’t minded at all, his father had rolled his eyes and called him an idiot and his brother had laughed that ‘of _course_  you wouldn’t settle for your own kind’ but overall they had welcomed Cas in with open arms. 

It was the school that had been the problem. At first a rival Alpha had challenged him, some douchbag called Zachariah, after that Cas’ entire family practically cast him out. Though it hadn’t been official, until this morning. 

Cas had slid into his cave, darted up to him in a blur of blue and laughter, practically freaking tackled him as he flailed around in confusion babbling that he was finally free, they had finally cast him out. 

As it turns out Cas’ lips are as soft and plump as they seem, warm against his own. 

He’s not sure it’s something Cas should be happy about, his family throwing him out but the omega was all but burrowing against him, sweet kisses that lapped into his mouth, purring low and happy. 

“We can officially mate, Dean.”

And right, holy shit right! Fuck he is an idiot because Cas is watching him all fond and amused and he may be blushing a little, muttering that that wasn’t the first thing he’d thought of, okay? 

Still the idea - He shivered, slid his fingers over the smooth expanse of Cas’ waist, pulled him close and kissed him properly, sucked and nipped his way into the merman's mouth, grinning all the while.

They’d discussed it before, much to his amusement (Cas had blushed and gotten so flustered, tail swaying nervously) about how this would work. Sex that is, their mating. Cas didn’t have the tight - uh- holes and Dean wasn’t too fond of the whole lay eggs squirt and go thing Cas’ kind were so fond of, and that’s when Cas had told him, stammering and fiddling with his webbed fingers that well - Mermaids had this little trick. 

If he moved onto dry enough land, say the ledge of Deans cave, up into the air and out of the ocean then his tail would split into legs and he would have a tight little hole just ripe for fucking. 

Dean was already edging him there, their kiss slipping messy and eager, his tentacles sliding to curl around the merman's body, teasing and caressing each inch they could. 

It wasn’t a difficult task to wrap around Cas and lift him from the rapidly shallowing water onto the rocks, watching the way water slid from pink tinged skin and dripped from Cas’ tail. 

Cas kissed him the entire time, Dean hauled up with his arms as Cas lent down, moaning low at the taste of him. 

He was already so eager, cock unsheathing and dripping with it, dragging his tentacle up and over one firm muscled leg with a low keen. 

Cas looked gorgeous, pulling up and shifting, legs dangling over the edge, bent back and leaning on his elbows, eyes blown wide and thighs parted, his cock stood stiff and proud. 

“Fuck, Cas, look atcha, you’re so damn pretty.”

He groaned when Cas whimpered softly, muscles jumping as he sucked in a sharp breath, pert ass hanging just from the ledge, Dean’s tentacles already fondling the firm flesh, squeezing and kneading playfully just to watch as the omega threw his head back and mewled. 

Cas’ tight hole was already slick, one of the beauty's of his magical transition, clenching around nothing practically fucking winking at him as Dean dipped down, slid under the ledge, breathing deep as he slid one tentacle up and up Cas’ thigh, dragged it down the crevice of Cas’ ass and traced the wet rim with the tip. 

Cas was so sensitive too, let out the most beautiful sound as Dean toyed with him, worked just the very tip of one tentacle into that tight hole, circled and stretched and worked him open nice and slow. 

It was ... something, fuck, amazing, it made his cock ache and his skin tingle, each tentacle trembling as it moved, curling about Cas’ legs, pulling him open wider, exposing him to Dean’s hungry gaze, watching avidly as Cas opened, watched as he pushed into the wet heat of him, that pink rim taut around his limb. 

Fuck it was hot, the sounds Cas made as he pumped, fucked him nice and full, flicked another, smaller tentacle around Cas’ sensitive rim, curled the thicker one until he was milking the omega’s prostate making him scream and cry and writhe under him. 

He pulled himself up, pushed over the omega, careful of how much water he dripped as he caught the mans mouth, fucked into it with his tongue, mimicking the movements he made as Cas rode him to release, grabbed for his shoulders and hair and back, blunt nails dragging red welts down his skin as Cas keened and clenched, arching up under him. 

He came with two tentacles pumping in and out of him, working him open and gaping as Cas gasped for air into Dean’s desperate mouth, cock pulsing between them, thick stripes of cum hitting Dean’s skin. 

He pulled away swearing, his own cock jerking at the sight of Cas completely pliant, mouth slack and swollen, rim obscene in the way it opened as he pulled his tentacles free. 

It took too much to be careful, wrapping his stronger limbs around his mate, lifting the sex limp omega up and just above the splashing waves, jerking his hips up as he pulled Cas down and onto his straining cokc. 

Fuck it was like heaven, Cas’ body pulling him deeper so fucking hot and needy around him, leaving him breathless as he fucked up and claimed his mate with each hard thrust. 

They were uncoordinated, jerky and rough, burying his face in the crook of Cas’ neck as arms pulled him closer, Cas’ little whimpers and moans pushing him closer to the edge. 

It was over too soon, a slick heat that uncurled at the very tips of him, had him doubling over and sinking his teeth into the soft flesh at that dip between shoulder and neck, marking his claim into his mate as he came, throbbing and spilling deep into Cas’ clenching ass. 

They were both gasping when he gently lowered Cas back into the water, grinned when the omega whined and arched, tail slipping between Dean’s gripping tentacles, slapping playfully at him as Cas smiled, crooked and lazy. 

“I love you, Alpha.”

He flushed, high on his cheek bones and pressed his response to Cas’ reddened lips. 

“Love you too, Cas.”


End file.
